The iris is an anatomic structure that defines and surrounds the pupillary aperture that allows light into the eye's interior. Pigment in the iris, specifically the amount and color of the pigment, determines human eye color. The primary function of the iris, along with the eyelids, is to control the amount of light that reaches the retina. Excessive exposure to sunlight may contribute to cataracts and age-related macular degeneration. People with insufficient pigment in the iris are prone to these diseases and to poor vision from glare and lens effects from the rim of the human lens. The greater the amount of pigment in the eye, the darker the color of the iris. Darker iris color provides greater protection from ultraviolet (“UV”) light and makes eyes less sensitive to bright light. Most of the world's population has darker eye color.
In addition to the biological function, the iris is the eye's most significant cosmetic feature. Color and patterns in the iris contribute to the belief that the eyes are the “window to the soul.”
Historically, radial tinted contact lens have been the primary method used to adjust the apparent color of the iris, but contact lenses have substantial and well-recognized limitations in this regard. For example, contact lenses are typically readily distinguishable from natural eye color. The lenses “float”, thereby moving the tinted portion over the pupil and causing the eyes to appear to be looking in different directions. Contact lenses also present risks of infection to the cornea, which in turn can lead to scarring and poor vision. Contact lenses are inconvenient, because they generally should be removed on a daily basis to minimize the risk of infection. Even so, contact lenses are not a viable option for a significant portion of the population, including those with dry eyes or other intolerance factors.
Substantial research and clinical study exist with respect to eye implants for purposes of improving the refractive performance of an eye and thereby improving vision. These corrective implants are transparent and often involve positioning within or near the pupillary axis—the eyes direct line of sight. The implants are shaped and dimensioned to modify the angulation of light rays passing through the cornea to change the eye's refractive properties.
A new permanent or semi-permanent alternative means of coloring the eye would have several immediate benefits. Eliminating the need for contact lenses would eliminate contact lens-related infections and problems that result from mishandling, such as leaving a lens in the eye too long. Darkening the cornea of those with little or no iris color due, for example, to genetic circumstances would reduce excessive sunlight exposure to the retina, improve vision and provide a desirable cosmetic enhancement. Using corneal opacification to make light exposure relatively uniform in those with surgical or traumatic irregularities of the iris would provide similar benefits. Mitigating iris color flaws would improve self-image and potentially improve vision. Providing a widely available means of cosmetically enhancing eye color would provide a means for self-expression and potentially improve vision.
“Aberration” is distortion in the shape of the cornea leading to misdirection of the light ray off the desired path to the center of vision the macula. A common form of aberration is called spherical aberration and is the tendency of the cornea to curve away from the midline or visual axis too quickly. This leads to progressive steepening at the rim and near sightedness that is greater at the rim than the center.
Wavefront analysis is performed by an aberometer. The aberometer can detect optical errors at a fine level. Wavefront analysis assesses every ray of light that enters the eye and then determines what changes will produce the clearest image. Aberometers precisely measure the overall refractive error of the entire eye and point out common errors of refraction that are not apparent to the older methods. The peripheral part of the cornea is a cause of aberration in many eyes and this is uncovered with dilation of the pupil with these instruments. Spherical aberration and its variants are the common finding in many eyes.